The invention relates to a drilling tool, in particular a rock-drilling tool.
Rock drills comprise a drill head, usually provided with a carbide cutting plate, a single-start or multi-start, spiral-like conveying helix, which adjoins said drill head, and a following clamping shank for fastening in a drive machine. In rock drills, the main task of the conveying helix is to convey out of the drill hole the material detached by the carbide cutting edge, i.e. the drilling dust or drillings. In this case, the size of the drilling-dust groove, i.e. the free conveying cross section, is critical for the capacity of the drill, i.e. good drilling-dust transportation ensures good advancement and prevents chatter marks in the drill hole and damage to the drill by jamming, overheating or the like. It is also the case that the service lives of a drilling tool are influenced by the good conveying properties of the drilling-dust groove.
Furthermore, the conveying helix also has to satisfy guidance properties of the drilling tool in the drill hole.
The helical discharge groove for drilling dust of a single-start or multi-start conveying helix is bounded on both sides by likewise helically running webs. In this case, the webs form a carrying surface or transporting surface for the drilling dust, said surface being oriented in the transporting direction of the drilling dust i.e. in the direction of the clamping shank. The circumferential surface or lateral surface of a web forms the so-called spine surface, with a certain spine width, of the web. The wider this spine surface, the better are the guidance properties of the drilling tool in the drill hole. The disadvantage here, however, is the increased friction in the drill hole and the reduced groove volume for transporting away the drilling dust. Accordingly, comprises have to be made between width of the spine surface of the webs and the resulting groove volume, on the one hand, and the required guidance properties, on the other hand.
The figures in DE-B 20 13 328 illustrate the basic construction of such a two-start conveying helix.
There are a number of proposals for improving the conveying properties of the drilling dust in the drilling-dust grooves. For example, EP 0 126 409 B2 makes provision for increasing the height of the leads of the conveying helixes in the direction of the clamping end in order thus to make available, in the region of the drill head, an increased number of web surfaces for the purpose of improving the guidance properties. This also increases the drilling-dust groove in the direction of the clamping end, i.e. in the conveying direction of the drilling dust, with the result that jamming of the drill cannot occur.
It is disclosed in DE 30 14 693 C2 that good conveying properties of a conveying helix in accordance with the principle of a conveying worm are only provided when the frictional resistance between the wall of the drill hole and the drillings located in the discharge groove is greater than between the drillings and the surface of the discharge groove. It would be necessary, for this purpose, for the volume of the drilling-dust groove to be constantly adapted to the quantity of drilling dust arising, in order to provide these friction ratios. This is not possible, however, on account of the different quantities of drilling dust arising on account of different drilling conditions. This state of the art thus proposes to increase the drilling-dust groove in sections in the direction of the clamping end.
DE-43 38 667 A1 has disclosed a rock drill in which a reduction in the wall friction is produced in that the spine surfaces of the spiral-like webs have grooves introduced therein. These secondary grooves predominately cause a reduction in the surface area of the web spines and thus reduce the friction. To a certain extent, they may also serve for discharging drillings, although this constitutes merely a secondary effect.
The object of the invention is to provide a drilling tool which, in relation to conventional drilling tools, has improved conveying properties for the drillings, along with reduced wall friction. In this case, the desired success is to be brought about by design measures which are as straightforward, and thus as cost-effective, as possible.
The invention is based on the finding that good conveying properties of the drilling dust in drilling-dust grooves are also determined not least by the size of the available drilling-dust-carrying surfaces. This size is determined by the number of discharge grooves, each with an associated web with carrying surface, present. A sufficient number or quantity of drilling-dust-carrying surfaces are formed by the flanks of helically running webs, said flanks being arranged essentially perpendicularly to the longitudinal axis of the drill. The design of the drilling tool according to the invention makes provision for providing, in addition to the conventionally provided main webs with corresponding carrying surfaces, conveying elements such as secondary webs or secondary flanks, which, for their part, form additional drilling-dust-carrying surfaces. In this case, the secondary webs may be designed similarly to the main webs. However, their external diameter is basically smaller than the external diameter of the conveying helix, with the result that there is a reduction in the frictional losses, along with improved conveying properties. It is also possible to provide core indents for the purpose of forming additional carrying surfaces or conveying edges for drilling dust.
By virtue of measures according to the invention, it is possible for the discharge groove to be formed as a so-called double groove or multiple groove, with the result that a plurality of individual grooves with associated carrying surfaces for drilling dust are preferably provided within one discharge groove.
This basic finding has led to a large number of possible designs for realizing this basic idea. These possible designs contain a variation in the manner of arranging the secondary webs and/or the secondary carrying surfaces in the form of secondary conveying edges. It is also possible to vary the number of such secondary conveying elements, this also resulting not least in the discharge groove being divided up into discharge sub-grooves of the same size or of different sizes and with groove depths of the same size or of different sizes.
Different embodiments of the basic idea according to the invention are explained in more detail in the following description and are illustrated in the drawing, in which: